The present invention relates to a battery comprising a cathode, an anode and an electrolyte, and more particularly to a battery which provides motive power using a lithium composite oxide as a cathode and lithium (Li) as a reacting species of the battery.
In recent years, many portable electric devices, such as camera-incorporated VTRs (Videotape Recorder), cellular phones, and laptop computers, become widespread, and miniaturization and weight saving thereof are developed. Concurrently, research and development has actively been advanced in order to improve an energy density of batteries and especially of secondary batteries, which are used as a portable power supply for these electric devices. Specifically, lithium secondary batteries and lithium ion secondary battery are promising, because they provide an energy density higher than ones of conventional lead batteries and conventional nickel-cadmium batteries.
As a cathode active material of the lithium secondary batteries and the lithium ion secondary batteries, lithium cobalt composite oxides containing lithium and cobalt (Co) and lithium nickel composite oxides containing lithium and nickel (Ni) are used, because these materials have various excellent properties such as a discharge capacity. However, in the lithium secondary batteries and the lithium ion secondary batteries using these lithium composite oxides, when a battery voltage is 4.25 V or more, the lithium composite oxide is degraded, and many properties such as storage stability and a charge and discharge cycle characteristic become low.
Thus, the battery voltage at charging these secondary batteries is set to 4.2 V or less.
However, developments of anodes progress every moment every day, the capacity thereof is improved, materials having a new charge and discharge profile are found, and simultaneously the voltage higher than 4.2 V has been desired. Moreover, generally, the energy densities of the lithium secondary battery and the lithium ion secondary battery depend on the battery voltage, so that the secondary batteries with the battery voltage of 4.2 V or less hardly satisfy ever-increasing demands to the energy density, which is a problem. Therefore, increasing the battery voltage is an important subject for the lithium secondary batteries and the lithium ion secondary batteries.
The present invention has been achieved to solve the above problems. It is an object of the invention to provide a battery with a high battery voltage at charging and an improved energy density.